This invention relates to improved fluid seals especially suitable for use in oil well drilling equipment in which fluid pressures of drilling mud, an abrasive slurry, may reach the magnitude of 5000 psi and temperatures may reach the magnitude of 200.degree. F.
In a typical oil drilling apparatus, the rotating equipment, from top to bottom, begins at the swivel and extends down the string to the point where the bit contacts the bottom of the bore hole. The swivel assembly sustains the weight of the drilling string, permits its rotation, and affords a rotating pressure seal and passageway for circulating drilling mud into the top of the string. The kelly, which is connected to the stem of the swivel, transmits torque from the rotary to the drilling string and permits the string to be moved vertically as the string is lowered when making a hole. The kelly is also the unit through which drilling mud is pumped down the string. Drilling mud is usually a mixture of weighting materials, clay, chemicals and water or oil and is thus an abrasive slurry.
Within the system itself, travel of drilling mud is typically from the mud pit (a storage area) to the slush or mud pump, from the pump through a standpipe and kelly hose to the swivel and into the kelly via a wash pipe in the swivel and the stem, also in the swivel, and down the drill string to the bit, up the annular space between the drill string and the borehole, through a blowout preventer stack to the return flow line, to a shale shaker for cuttings removal, to a settling pit, and then to temporary storage in a sump pit.
The swivel generally contains the hollow stem to which the kelly is attached, the stem being journalled in spaced bearings to permit its rotation. The stem is connected to the kelly hose and the wash pipe through which the drilling mud is supplied by a pump from the supply. A packing is associated with the juncture of the stem and the wash pipe, and is constructed to permit relative rotation therebetween. The packing contains multiple elastomeric packing rings constrained within a packing housing. The stem and the kelly (and thus the drilling string) rotate at speeds up to about 400 rpm.
Because of the abrasive nature of the drilling mud, and the relatively high pressures and temperatures encountered, the packings have limited life, for example, on the order of 3 days to 3 weeks. Replacement and repair of the packings is a time consuming and expensive operation, requiring the interruption of the drilling operation, disasembly of the swivel, and reconstruction of the swivel.